The prevailing method for treatment of industrial waste containing hazardous metals consists of mixing it with cement and kneading the resulting mixture with water, followed by curing and solidification, so that hazardous metals are stabilized to prevent their leaching. However, simply solidifying industrial waste with cement involves several problems associated with secondary pollution, unless its application is limited. For example, when treatment with cement according to the prior art technology is applied to fly ash collected by an electrostatic precipitator or bag filter at the time of waste incineration, it cannot completely prevent the leaching of lead contained therein in high concentrations. To make matters worse, lead in the ash of waste is more liable to leaching in the alkaline environment, as known well. Since the incinerator for municipal solid waste is fed with slaked lime to suppress the evolution of hydrochloric acid, it gives rise to fly ash containing calcium compounds, such as slaked lime (or calcium hydroxide), calcium chloride (as a reaction product of slaked lime and hydrochloric acid), and calcium oxide (resulting from the heating of slaked lime). Fly ash collected by an electrostatic precipitator or bag filter under such operating conditions contains a large amount of leachable lead. With the prior art technology, it is impossible to completely prevent the leaching of lead. Therefore, at the present time, it is common practice to dump such fly ash without hazardous metals being fully stabilized, and such dumping is presenting problems associated with secondary pollution.
It has become apparent inside and outside the country that it is difficult to stabilize industrial waste containing hazardous metals so as to prevent their leaching by simple solidification with cement. This has stimulated the development of a new waste treatment method which permits safe dumping on land and at sea without the possibility of heavy metals leaching out to cause secondary pollution.
The present invention was completed in view of the current state of waste treatment. Accordingly, it is an object of the present invention to provide a waste treatment method capable of certainly solidifying and sealing industrial waste containing hazardous metals, thereby stabilizing it such that hazardous metals will not leach out after dumping.